Cmp Polishing Slurry and Method of Polishing Substrate

ABSTRACT

The present invention relates to a CMP polishing slurry comprising cerium oxide particles, a dispersant, a water-soluble polymer and water, wherein the water-soluble polymer is a polymer obtained in polymerization of a monomer containing at least one of a carboxylic acid having an unsaturated double bond and the salt thereof by using at least one of a cationic azo compound and the salt thereof as a polymerization initiator. The present invention provides a polishing slurry and a polishing method allowing polishing efficiently uniformly at high speed without scratch and also allowing easy process management in the CMP technology of smoothening an interlayer dielectric film, BPSG film, and insulation film for shallow trench isolation.

TECHNICAL FIELD

The present invention relates to a CMP polishing slurry for use in asubstrate surface-smoothening step in production of semiconductordevices, in particular in steps of smoothening an interlayer dielectricand BPSG (silicon dioxide film doped with boron and phosphorus) film,forming a shallow trench isolation, and others, and a method ofpolishing a substrate by using the CMP polishing slurry.

BACKGROUND ART

Currently under research and development are processing methods forimprovement in density and miniaturization in production of ULSIsemiconductor devices. One of the methods, chemical mechanical polishing(CMP) technology is now a technology essential in production ofsemiconductor devices, for example, for smoothening of an interlayerdielectric, forming a shallow trench device isolation, and formingplugged and embedded metal wiring.

In conventional production of semiconductor devices, inorganicinsulation film layers such as a silicon oxide insulation film areformed by methods such as plasma CVD and low-pressure CVD. Polishingslurries of fumed silica are commonly studied as a chemical mechanicalpolishing slurry for use in smoothening of the inorganic insulation filmlayer. The fumed silica polishing slurries are produced by grain growth,for example, by oxidative thermolysis of tetrachlorosilane andsubsequent pH adjustment. However, such an polishing slurry still has aproblem that the polishing speed is lower.

Shallow trench isolation has been used for isolation of devices in anintegrated circuit in the generation of a design rule of 0.25 μm orlater. In the shallow trench isolation, CMP is used for removal ofexcessive silicon oxide films formed on a substrate and a stopper filmsmaller in polishing speed is formed under the silicon oxide film fortermination of polishing. For example, silicon nitride is used for thestopper film, and the difference in polishing speed between the siliconoxide film and the stopper film is preferably greater. Conventionalcolloidal silica-based polishing slurries have a smaller polishing speedratio between the silicon oxide film and the stopper film atapproximately 3, and thus, did not have properties practically usablefor shallow trench isolation.

On the other hand, cerium oxide polishing slurries have been used aspolishing slurries for glass surface such as of a photomask and lens.Cerium oxide particles are softer than silica or alumina particles, lesslikely to cause scratching on the polishing surface and thus, useful forfinishing mirror-surface polishing. The particles also have an advantagethat the polishing speed therewith is faster than that of silicapolishing slurries. Recently, CMP polishing slurries for semiconductorprocessing, containing a high-purity cerium oxide abrasive have beenused. Such methods are described, for example, in Japanese PatentApplication Laid-Open No. 10-106994.

Also known is a fact that an additive is added for control of thepolishing speed with a cerium oxide polishing solution and forimprovement in global smoothness. Such methods are described, forexample, in Japanese Patent Application Laid-Open No. 8-22970.

SUMMARY OF THE INVENTION

However, the polishing slurries containing cerium oxide still have aproblem that it is not easy to perform high speed polishing whilemanaging the polishing process. The present invention provides apolishing slurry and a polishing method allowing polishing of a siliconoxide film or the like at high speed without polishing scratch and alsoallowing easy process management in the CMP technology of smoothening aninterlayer dielectric film, BPSG film, and insulation film for shallowtrench isolation.

The present invention relates to (1) a CMP polishing slurry comprisingcerium oxide particles, a dispersant, a water-soluble polymer and water,wherein the water-soluble polymer is a polymer obtained inpolymerization of a monomer containing at least one of a carboxylic acidhaving an unsaturated double bond and the salt thereof by using at leastone of a cationic azo compound and the salt thereof as a polymerizationinitiator.

The present invention relate to (2) the CMP polishing slurry accordingto (1), wherein the blending amount of the water-soluble polymer is 0.01weight part or more and 5 weight parts or less with respect to 100weight parts of the CMP polishing slurry.

The present invention relates to (3) the CMP polishing slurry accordingto (1) or (2), wherein the weight-average molecular weight of thewater-soluble polymer is 200 or more and 50,000 or less.

The present invention relates to (4) the CMP polishing slurry accordingto any one of (1) to (3), wherein the average particle diameter of thecerium oxide particles is 1 nm or more and 400 nm or less.

The present invention relates to (5) the CMP polishing slurry accordingto any one of (1) to (4), wherein the blending amount of the ceriumoxide particles is 0.1 weight part or more and 5 weight parts or lesswith respect to 100 weight parts of the CMP polishing slurry.

The present invention relates to (6) the CMP polishing slurry accordingto any one of (1) to (5), wherein the pH thereof is 4.5 or higher and6.0 or lower.

The present invention relates to (7) a polishing method of substratecomprising: pressing a substrate having a film to be polished against apolishing cloth of a polishing table; and polishing the film to bepolished by moving the substrate and the polishing table relatively toeach other while supplying the CMP polishing slurry according to any oneof (1) to (6) between the film to be polished and the polishing cloth.

The present invention provides a polishing slurry and a polishing methodallowing polishing of a silicon oxide film or the like uniformly at highspeed without polishing scratch and also allowing easy processmanagement in the CMP technology of smoothening films such as aninterlayer dielectric film, BPSG film, and insulation film for shallowtrench isolation.

The disclosure of this application is related to the subject matterdescribed in Japanese Patent Application No. 2004-216039 filed on Jul.23, 2004, the disclosure of which is incorporated by reference herein.

BEST MODE OF CARRYING OUT THE INVENTION

Generally, cerium oxide is obtained by oxidation of a cerium compoundsuch as carbonate salt, nitrate salt, sulfate salt, or oxalate salt. Acerium oxide polishing slurry for use in polishing a silicon oxide filmformed by TEOS CVD or other method allows higher-speed polishing, butcauses more polishing scratches, when the crystal diameter of theparticle becomes greater and the crystal distortion is smaller, i.e.,when the crystallinity thereof is higher. Although the method ofproducing cerium oxide particles for use in the present invention is notparticularly limited, the crystal diameter of the cerium oxide ispreferably 5 nm or more and 300 nm or less. The content of alkali metalsand halogens is preferably reduced to 10 ppm or less in the cerium oxideparticle because the particle is used for polishing during production ofsemiconductor devices.

In the present invention, cerium oxide powder can be prepared, forexample, by calcination, oxidation with hydrogen peroxide, or the like.The calcining temperature is preferably 350° C. or higher and 900° C. orlower.

The cerium oxide particles prepared by the method are aggregate, andthus, preferably pulverized mechanically. The pulverization method ispreferably a dry pulverization method, for example by using a jet mill,or a wet pulverization method, for example by using a planetary beadmill. The jet mill is described, for example, in Kagaku Kogaku Ronbunshu(Chemical Industrial Paper Collection), vol. 6, No. 5 (1980) pp. 527 to532.

A method of dispersing such cerium oxide particles in water that is amain disperse medium includes, for example, a method of usinghomogenizer, ultrasonic dispersing machine, or wet process ball mill,aside from a method of dispersion process by using an ordinary agitator.

Further microparticulating the cerium oxide dispersed by the abovemethod is prepared by a sedimentation classification method of leavingthe cerium oxide dispersion for a long period allowing sedimentation oflarger particles and withdrawing the supernatant liquid by a pump.Besides, a high pressure homogenizer may be used for collision of thecerium oxide particles in the disperse medium mutually at high pressure.

The average particle diameter of the cerium oxide particle thus preparedin the CMP polishing slurry is preferably 1 to 400 nm, more preferably 1to 300 nm, and still more preferably 1 to 200 nm. An average particlediameter of cerium oxide particles of less than 1 nm may lead todecrease in polishing speed, while an average particle diameter of morethan 400 nm may lead to more frequent scratching on the polished film.In the present invention, the average particle diameter of cerium oxideparticles is the D50 value (median diameter of volumetric distribution,cumulative median value), as measured in a laser-diffraction particlesize distribution analyzer.

The CMP polishing slurry according to the present invention is prepared,for example, by blending the cerium oxide particles having theproperties above, a dispersant and water to disperse the particles andadding a water-soluble polymer additionally. The concentration of thecerium oxide particles is preferably in the range of 0.1 weight part ormore and 5 weight parts or less, more preferably 0.2 weight part or moreand 2 weight parts or less, and still more preferably 0.5 weight part ormore and 1.5 weight parts or less, with respect to 100 weight parts ofthe CMP polishing slurry. An excessively lower concentration leads todecrease in polishing speed, while an excessively higher concentrationleads to aggregation.

Examples of the dispersants for use include water-soluble anionicdispersants, water-soluble nonionic dispersants, water-soluble cationicdispersants, water-soluble amphoteric dispersants, and the like. Polymerdispersants containing an ammonium acrylate salt as the copolymerizationcomponent are also favorable. Examples thereof include ammoniumpolyacrylate, copolymers of acrylic amide and ammonium acrylate, and thelike.

Two or more dispersants, containing at least one polymer dispersantcontaining an ammonium acrylate salt as the copolymerization componentand at least one dispersant selected from water-soluble anionic,nonionic, cationic, and amphoteric dispersants, may be used incombination. Because the dispersant is used in abrasion duringproduction of semiconductor devices, the content of alkali metals suchas sodium and potassium ions, halogen atoms and a sulfur atom in thedispersant is preferably reduced to 10 ppm or less.

Examples of the water-soluble anionic dispersants includetriethanolamine laurylsulfate, ammonium laurylsulfate, triethanolaminepolyoxyethylene alkylether sulfate, special polycarboxylate polymerdispersants, and the like.

Examples of the water-soluble nonionic dispersants includepolyoxyethylene laurylether, polyoxyethylene cetylether, polyoxyethylenestearylether, polyoxyethylene oleylether, polyoxyethylene higher-alcoholether, polyoxyethylene octylphenylether, polyoxyethylenenonylphenylether, polyoxyalkylene alkylether, polyoxyethylenederivatives, polyoxyethylene sorbitan monolaurate, polyoxyethylenesorbitan monopalmitate, polyoxyethylene sorbitan monostearate,polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitanmonooleate, polyoxyethylene sorbitan trioleate, polyoxyethylene sorbitoltetraoleate, polyethylene glycol monolaurate, polyethylene glycolmonostearate, polyethylene glycol distearate, polyethylene glycolmonooleate, polyoxyethylene alkylamine, polyoxyethylene hydrogenatedcastor oil, 2-hydroxyethyl methacrylate, alkyl alkanol amides, and thelike.

Examples of the water-soluble cationic dispersants includepolyvinylpyrrolidone, coconutamineacetate, stearylamineacetate, and thelike.

Examples of the water-soluble amphoteric dispersants include laurylbetaine, stearyl betaine, lauryldimethylamine oxide,2-alkyl-N-carboxymethyl-N-hydroxyethylimidazoliniumbetaine, and thelike.

The amount of these dispersants added is preferably in the range of 0.01weight part or more and 10 weight parts or less with respect to 100weight parts of the cerium oxide particles, for improvement ofdispersion and prevention of sedimentation of the particles in thepolishing slurry and for a relation of polishing scratch and the amountof the dispersants. The molecular weight of the dispersant is preferably100 to 50,000, more preferably 1, 000 to 10,000. A dispersant having amolecular weight of less than 100 may cause decrease in the polishingspeed when a silicon oxide or nitride film is polished, while adispersant having a molecular weight of more than 50,000 may lead toincrease in viscosity and deterioration in the storage stability of theCMP polishing slurry.

The water-soluble polymer according to the present invention is apolymer obtained by radical polymerization of at least one monomer of acarboxylic acid having an unsaturated double bond and the salt thereofby using at least one of a cationic azo compound and the salt thereof asa polymerization initiator, and the polymer may be a copolymer.

Examples of the carboxylic acids having an unsaturated double bondinclude acrylic acid, methacrylic acid, crotonic acid, vinylacetic acid,tiglic acid, 2-trifluoromethylacrylic acid, itaconic acid, fumaric acid,maleic acid, citraconic acid, mesaconic acid, gluconic acid, and thelike, and these carboxylic acids may be used in combination of two ormore. The salts of the carboxylic acid include ammonium, potassium, andalkylamine salts.

The polymer may be a copolymer of the carboxylic acid and/or the saltthereof with a radical polymerizable monomer such as C₁ to C₁₈ acrylicester, C₁ to C₁₈ methacrylic ester, acrylamide, vinylalcohol,acrylonitrile, vinylpyrrolidone, or vinylpyridine.

Examples of the cationic azo compounds according to the presentinvention and the salts thereof include2,2′-azobis[2-(5-methyl-2-imidazolin-2-yl)propane]hydrochloride,2,2′-azobis[2-(2-imidazolin-2-yl)propane],2,2′-azobis[(2-(2-imidazolin-2-yl)propane] hydrochloride,2,2′-azobis[2-(2-imidazolin-2-yl)propane]sulfate hydrate,2,2′-azobis[2-(3,4,5,6-tetrahydropyrimidin-2-yl)propane]hydrochloride,2,2′-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane}hydrochloride,2,2-azobis(2-amidino propane) hydrochloride,2,2′-azobis(2-methylpropionamidoxime), and the like. These compounds maybe used in combination of two or more, and organic salts thereofsuchasacetate, oxalate, malonate, succinate, malate, tartarate, andcitrate and inorganic salts such as phosphate, hydrobromide,hydroiodide, and hydrofluoride are also usable.

The solvent used during polymerization is not particularly limited, but,water or C₁ to C₄ alcohols such as methanol, isopropanol, propanol, andbutanol are preferable, and these solvents may be used in combination.

The weight-average molecular weight of the water-soluble polymer thusobtained is preferably in the range of 200 or more and 50,000 or less,more preferably 300 or more and 20,000 or less, and most preferably 500or more and 10,000 or less. A molecular weight of. less than 200 maylead to insufficient smoothening efficiency, while a molecular weight ofmore than 50,000 may lead to aggregation of cerium oxide particles. Inaddition, a mercapto compound-based molecular weight adjustor such asmercaptoethanol may be used. The blending amount of the water-solublepolymer according to the present invention is preferably in the range of0.01 weight part or more and 5 weight parts or less, more preferably0.05 weight part or more and 3 weight parts or less, and most preferably0.1 weight part or more and 1 weight part or less, with respect to 100weight parts of the CMP polishing slurry. An excessively smalleraddition amount leads to decrease in smoothening efficiency, while anexcessively large amount leads to aggregation of cerium oxide particles.

The polishing slurry according to the present invention may containanother water-soluble polymer. The another water-soluble polymer is notparticularly limited, and examples thereof include polysaccharides suchas alginic acid, pectin acid, carboxymethylcellulose, agar, curdlan andpullulan; polycarboxylic acids such as polyaspartic acid, polyglutamicacid, polylysine, polymalic acid, polyamide acid, polyamide acidammonium salt, polyamide acid sodium salt and polyglyoxylic acid and thesalt thereof; and vinyl polymers such as polyvinylalcohol,polyvinylpyrrolidone and polyacrolein. The weight-average molecularweight of the water-soluble polymer is preferably 500 or more, and theblending amount thereof is preferably in the range of 0.01 weight partor more and 5 weight parts or less with respect to 100 weight parts ofthe CMP polishing slurry.

The polishing slurry according to the present invention shows stabilizedproperties even when it is stored as a two-liquid CMP polishing slurrycomposed of a cerium oxide slurry containing cerium oxide particles, adispersant and water and an additional solution containing awater-soluble polymer and water, and also even when it is stored as apolishing slurry previously containing the water-soluble polymer. Whenthe polishing slurry is stored as the two-liquid polishing slurrycomposed of a cerium oxide slurry and an additional solution, it ispossible to adjust the smoothening efficiency and the polishing speedeasily by changing the blending ratio of these two liquids. Duringpolishing with the two-liquid polishing slurry, the additional solutionand the cerium oxide slurry are fed to a polishing table as they aresupplied separately from different pipes and mixed immediately before asupply pipe outlet where these pipes are connected, or the additionalsolution is mixed with the cerium oxide slurry immediately beforepolishing.

The CMP polishing slurry according to the present invention is used forpolishing after it is adjusted to a desirable pH. A pH adjuster for useis not particularly limited, but ammonia water or an acid component isused more favorably than alkali metals when the polishing slurry is usedfor semiconductor polishing. The pH may be adjusted with the ammoniumsalt of the water-soluble polymer previously partially neutralized withammonia. The pH of the CMP polishing slurry is preferably 4.5 or moreand 6.0 or less, more preferably 4.8 or more and 5.6 or less. Anexcessively low pH leads to decrease in polishing speed, while anexcessively high pH leads to deterioration in smoothness.

The pH of the CMP polishing slurry according to the present inventionwas measured by using a pH meter (for example, Model PH81, manufacturedby Yokogawa Electric Corporation) . After two-point calibration with astandard buffer solution (phthalate buffer solution, pH: 4.21 (25° C.)and a neutral phosphate buffer solution, pH: 6.86 (25° C.)), anelectrode was immersed in the CMP polishing slurry, and the pHstabilized after 2 minutes or more was measured.

The polishing method according to the present invention is characterizedby polishing a film to be polished by pressing a substrate having thefilm to be polished against a polishing cloth of a polishing table andmoving the substrate and the polishing tablerelatively to each otherwhile supplying the CMP polishing slurry according to the presentinvention to the space between the film to be polished and the polishingcloth.

Examples of the substrates include substrates for semiconductor deviceproduction, for example, substrates having an inorganic insulation layerformed on a semiconductor substrate such as a semiconductor substratehaving a circuit element and a wiring pattern formed thereon and asemiconductor substrate having a circuit element formed thereon.Examples of the films to be polished include the inorganic insulationlayers described above including a silicon oxide film layer, siliconnitride and silicon oxide film layers, and the like. Surfaceirregularity of the silicon oxide film layer is eliminated by polishingthe silicon oxide or nitride film layer formed on the semiconductorsubstrate with the CMP polishing slurry above, and the semiconductorsubstrate is smoothened over the entire surface. The substrate can alsobe used for shallow trench isolation. For use in shallow trenchisolation, the ratio of the silicon-oxide-film polishing speed to thesilicon-nitride-film polishing speed, i.e., silicon-oxide-film polishingspeed/silicon nitride film polishing speed, is preferably 10 or more.The difference between the silicon-oxide-film polishing speed and thesilicon nitride film polishing speed is small at a ratio of less than10, and it is difficult to stop abrasion at a predetermined positionduring shallow trench isolation. The polishing speed of the siliconnitride film becomes far smaller at a ratio of 10 or more, and thus, itis possible to stop abrasion easily and thus such a high ratio is morefavorable for shallow trench isolation. The substrate is preferablyprotected from scratching during polishing for use in shallow trenchisolation.

Hereinafterr the polishing method will be described, by taking asemiconductor substrate having an inorganic insulation layer formedthereon as an example.

In the, polishing method according to the present invention, a generalpolishing machine having a holder holding a substrate formed a film tobe polished such as a semiconductor substrate and having a polishingtable allowing attachment of a polishing cloth (pad) equipped with arotational frequency-adjustable motor or the like may be used as thepolishing machine. For example, a polishing machine: EPO-111,manufactured by Ebara Corporation may be used. The polishing cloth maybe common nonwoven fabric, expanded polyurethane, porous fluoroplastic,or the like, but is not particularly limited. The polishing cloth ispreferably processed to have grooves for holding the CMP polishingslurry. The polishing condition is not particularly limited, but therotational velocity of the polishing table is preferably lower at 200rpm or less for prevention of separation of the semiconductor substrate,and the pressure applied to the semiconductor substrate (processingload) is preferably not larger than 100 kPa for prevention of scratchingafter polishing. A CMP polishing slurry is supplied continuously ontothe polishing cloth, for example, by a pump during polishing. The feedrate is not particularly limited, but the surface of the polishing clothis preferably covered with the CMP polishing slurry all the time.

The semiconductor substrate after polishing is preferably washedthoroughly with running water and dried while the water dropletsremaining on the semiconductor substrate are removed, for example, witha spin drier. It is possible to eliminate surface irregularity and tomake the semiconductor substrate smoothened over the entire surface bypolishing the film, an inorganic insulation layer, to be polished withthe polishing slurry. After the smoothened shallow trench is formed,aluminum wiring is formed on the silicon oxide insulation film layer; asilicon oxide insulation film is formed between and on the wirings bythe method above; and the film is then surface-smoothened similarly bypolishing with the CMP polishing slurry. It is possible to produce asemiconductor substrate having a desired number of layers by repeatingthe step several times.

For global smoothening of an irregular-surfaced film to be polished(silicon oxide film), convex regions thereon should be polishedselectively. When the polishing slurry containing the water-solublepolymer according to the invention is used, a protection film is formedon the surface of the cerium oxide particles and the film to bepolished. Thus, the film to be polished in concave regions having asmaller effective polishing load is protected, but the film to bepolished on the convex regions having a greater effective polishing loadis selectively eliminated by polishing. In this way, it is possible toperform global smoothening, independently of the pattern on thepolishing surface. The water-soluble polymer according to the presentinvention, which has a polymerization initiator cationic azo compoundbound to its terminal, is adsorbed electrostatically on thenegatively-charged silicon oxide film in the weakly acidic to neutralrange. As a result, a protection film is formed on the surface of thefilm to be polished uniformly and efficiently, and the wafer surface ispolished uniformly.

The inorganic insulation film to which the CMP polishing slurryaccording to the invention is used is produced, for example, bylow-pressure CVD, plasma CVD, or the like. In preparing the siliconoxide film by low-pressure CVD, monosilane SiH₄ is used as a Si sourceand oxygen O₂ is used as an oxygen source. The film is obtained in theSiH₄—O₂ oxidation reaction at a temperature of 400° C. or lower. Thefilm is heat-treated as needed after CVD at a temperature of 1,000° C.or lower. When phosphorus P is doped for surface smoothening by hightemperature reflow, use of a SiH₄—O₂—PH₃ reaction gas is preferable. Theplasma CVD method has an advantage that the chemical reaction, whichdemands high temperature under normal thermal equilibrium, can becarried out at low temperature The plasma generation methods include twomethods: a capacitively coupled method and an inductively coupledmethod. The reaction gases include SiH₄—N₂O gas containing SiH₄ as theSi source and N₂O as the oxygen source; and a TEOS-O gas (TEOS-plasmaCVD method) containing tetraethoxysilane (TEOS) as the Si source. Thesubstrate temperature is preferably 250° C. to 400° C., and the reactionpressure is preferably in the range of 67 to 400 Pa. Thus, the siliconoxide film according to the present invention may be doped with anelement such as phosphorus or boron. Similarly, the silicon nitride filmis formed by low-pressure CVD at a high temperature of 900° C. in theSiH₂Cl₂—NH₃ oxidation reaction, while dichlorosilane SiH₂Cl₂ is used asthe Si source and ammonia NH₃ as the nitrogen source. The reaction gasused in the plasma CVD method is a SiH₄—NH₃ gas containing SiH₄ as theSi source and NH₃ as the nitrogen source. The substrate temperature ispreferably 300° C. to 400° C.

The CMP polishing slurry and the polishing method according to thepresent invention can be applied not only to the silicon oxide filmformed on a semiconductor substrate but also in the production processesfor various semiconductor devices. For example, they may be used forpolishing of silicon oxide films formed on a wiring board having apredetermined wiring; inorganic insulation films of glass, siliconnitride or the like; films mainly containing polysilicon, Al, Cu, Ti,TiN, W, Ta, TaN, or the like; optical glasses such as photomask, lens,and prism; inorganic conductive films such as ITO; optical integratedcircuit, photoswitching element, optical waveguides made of glass or acrystalline material; an end face of an optical fiber; optical singlecrystals such as scintillator; solid-state laser single crystals; bluelaser LED sapphire substrates; semiconductor single crystals such asSiC, GaP, and GaAs; , glass plates for magnetic disk; magnetism heads,and the like.

EXAMPLES Example 1 Synthesis of Water-Soluble Polymer

960 g of deionized water was placed in a 3-liter preparative flask andheated to90° C. while stirred under nitrogen gas atmosphere, and asolution of 497 g of acrylic acid and 53 g of2,2′-azobis[2-(2-imidazolin-2-yl)propane] in 500 g of methanol was addedinto the flask over a period of 2 hours. The mixture was then kept at90° C. for 3 hours, cooled, to give a water-soluble polymer solution.The nonvolatile matter therein was measured to be 25 weight %. Theweight-average molecular weight of the polyacrylic acid thus obtained,as measured with a HPLC pump (L-7100, manufactured by Hitachi) equippedwith a differential refractometer (L-3300, manufactured by Hitachi) anda GPC column (W550, manufactured by Hitachi Chemical Co., Ltd.) by using0.3 M NaCl as a mobile phase, was 5,000 (as polyethylene glycol).

(Preparation of Cerium Oxide Particles and CMP Polishing Slurry)

40 kg of cerium carbonate hydrate was placed in an alumina container andcalcined at 830° C. for 2 hours in air, to give approximately 20 kg of ayellow white powder. Phase analysis of the powder by X-ray diffractionshowed that the product was cerium oxide. The diameter of the calcinedpowder particles was 30 to 100 μm. 15 kg of the cerium oxide particlepowder was dry pulverized by use of a jet mill. After dry pulverization,the specific surface area of the polycrystalline material, as measuredby the BET method, was 9 m²/g.

10 kg of the cerium oxide powder and 39.875 kg of deionized water weremixed; 125 g of a commercially available aqueous ammonium polyacrylatesolution (weight-average molecular weight: 8,000) (40 weight %) wasadded thereto; and the mixture was dispersed under ultrasonication whilethe mixture was stirred. The ultrasonic wave frequency was 400 kHz, andthe dispersion period was 20 minutes. Then, 5 kg of the cerium oxidedispersion was placed and left in a 10-liter container, allowingsedimentation classification. After classification for 200 hours, thesupernatant liquid at a height of 110 mm or more from the containerbottom was withdrawn with a pump. The supernatant cerium oxidedispersion obtained was diluted with deionized water to a solid matterconcentration of 5 weight %, to give a cerium oxide slurry. The slurrywas diluted to a suitable concentration for measurement of the averageparticle diameter of the particles in the cerium oxide slurry, and theaverage particle diameter D50, as measured by using a laser-diffractionparticle size distribution analyzer Master Sizer Microplus (trade name,manufactured by Malvern) at a refractive index of 1.93 and an absorptionof 0, was 170 nm. The amount of impurity ions (Na, K, Fe, Al, Zr, Cu,Si, and Ti), as measured by an atomic absorption photometer AA-670G(manufactured by Shimadzu Corporation), was 1 ppm or less.

36 g of the aqueous polyacrylic acid solution thus prepared (25 weight%) and 2,364 g of deionized water were mixed, and the mixture wasadjusted to pH 4.8 with ammonia water (25 weight %). Then, 600 g of thecerium oxide slurry (solid matter: 5 weight %) was added thereto, togive a cerium oxide CMP polishing slurry (solid matter: 1.0 weight %).The polishing slurry had a pH of 5.0. The average particle diameter D50of the particles in the polishing slurry, as measured by alaser-diffraction particle size distribution analyzer after dilution toa suitable concentration, was 170 nm.

(Polishing of Insulation Film Layer)

A 864 wafer manufactured by SEMATECH (φ200 mm, SiN film thickness: 150nm, Sio2 film thickness: 610 nm in convex region and 610 nm in concaveregion) was used as a test wafer for evaluation ofshallow-trench-isolation (STI) insulation film CMP. The test wafer wasattached to a holder of a polishing machine (trade name: Mirra,manufactured by Applied Materials) having an adsorption pad for fixing asubstrate to be held, while a porous urethane resin polishing padIC-1000 (K groove) manufactured by Rodel was connected to a polishingtable of φ480 mm. The holder was placed on the pad with its insulationfilm face facing downward, and the pressures of membrane, retainer ring,and inner tube were respectively set to 3.0 psi, 3.5 psi, and 3.0 psi(20.6 Pa, 24.0 Pa, and 20.6 Pa) as the processing load. The test waferfor evaluation of the STI insulation film CMP was polished while thepolishing table and the wafer were moved respectively to each other at aspeed of 98 rpm and 78 rpm and the CMP polishing slurry thus preparedwas fed onto the polishing table dropwise at a rate of 200milliliter/minute. The end point of polishing was determined bymonitoring a torque current value of the polishing table. The waferafter polishing was washed thoroughly with purified water and thendried. The thickness of the residual insulation film in the concave andconvex regions, or the residual SiN film was measured by using anoptical interference thickness meter (trade name: Nanospec AFT-5100,manufactured by Nanometrics Inc.) . In addition, the difference in levelbetween the convex region and the concave region after polishing wasmeasured by using a level difference meter Dektak V200-Si manufacturedby veeco. The results are summarized in Table 1.

Example 2 Synthesis of Water-Soluble Polymer

960 g of deionized water was placed in a 3-liter preparative flask andheated to 90° C. while stirred under nitrogen gas atmosphere; a solutionof 497 g of acrylic acid and 103 g of2,2′-azobis(2-(2-imidazolin-2-yl)propane]bisulfate dihydrate in 500 g ofdeionized water was added into the flask over a period of 2 hours. Themixture was then kept at 90° C. for 3 hours, cooled to give awater-soluble polymer solution. The nonvolatile matter measured was 25weight %. The molecular weight measurement of the water-soluble polymerobtained similarly to Example 1 revealed that the weight-averagemolecular weight thereof was 3,200 (as polyethylene glycol).

(Preparation of Polishing Slurry)

48 g of the aqueous polyacrylate solution thus obtained (25 weight %)and 2,352 g of deionized water were mixed, and the mixture was adjustedto pH 5.3 with ammonia water (25weight %). Additionally, 600 g of thecerium oxide slurry (solid matter: 5 weight %) was added thereto, togive a cerium oxide-based CMP polishing slurry (solid matter: 1.0 weight%). The polishing slurry had a pH of 5.5, and the average particlediameter of the particles in the polishing slurry, as measured by alaser-diffraction particle size distribution analyzer after dilution toa suitable concentration, was 170 nm.

(Polishing of Insulation film Layer)

A test wafer for evaluation of shallow-trench-isolation (STI) insulationfilm CMP was polished in the same manner as in Example 1, except thatthe polishing slurry thus prepared was used. The results are summarizedin Table 1.

Example 3 Synthesis of Water-Soluble Polymer

360 g of deionized water was placed in a 3-liter preparative flask andheated to 90° C. while stirred under nitrogen gas atmosphere, and asolution of 256 g of methacrylic acid, 255 g of acrylic acid and 46 g of2,2′-azobis[2-(2-imidazolin-2-yl)propane] in 500 g of methanol was addedinto the flask over a period of 2 hours. The mixture was kept at 90° C.for 3 hours, cooled to give a water-soluble polymer solution. Then onvolatile matter determined was 25 weight %. The molecular weightmeasurement of the water-soluble polymer obtained similarly to Example 1revealed that the weight-average molecular weight thereof was 4,200 (aspolyethylene glycol).

(Preparation of Polishing Slurry)

36 g of the aqueous polyacrylic acid-methacrylic acid copolymer solutionobtained above (25 weight %) was mixed with 2,364 g of deionized water,and the mixture was adjusted to pH 4.9 with ammonia water (25 weight %). Additionally, 600 g of the cerium oxide slurry (solid matter: 5 weight%) was added thereto, to give a cerium oxide-based CMP polishing slurry(solid matter: 1.0 weight %). The polishing slurry had a pH of 5.1, andthe average particle diameter of the particles in the polishing slurry,as measured by a laser-diffraction particle size distribution analyzerafter dilution to a suitable concentration, was 170 nm.

(Polishing of Insulation Film Layer)

A test wafer for evaluation of shallow-trench-isolation (STI) insulationfilm CMP was polished in the same manner as in Example 1, except thatthe polishing slurry thus prepared was used. The results are summarizedin Table 1.

Example 4 Synthesis of Water-Soluble Polymer

960 g of deionized water was placed in a 3-liter preparative flask andheated to 90° C. while stirred under nitrogen gas atmosphere, and asolution of 256 g of methacrylic acid, 255 g of acrylic acid and 89 g of2,2′-azobis[2-(2-imidazolin-2-yl)propane]bisulfate dihydrate in 500 g ofdeionized water was added into the flask over a period of 2 hours. Themixture was kept at 90° C. for 3 hours, cooled to give a water-solublepolymer solution. The nonvolatile matter measured was 25 weight %. Themolecular weight measurement of the water-soluble polymer obtainedsimilarly to Example 1 revealed that the weight-average molecular weightwas 7,500 (as polyethylene glycol).

(Preparation of Polishing Slurry)

30 g of the aqueous polyacrylic acid-methacrylic acid copolymer solutionobtained above (25 weight %) was mixed with 2,370 g of deionized water,and the mixture was adjusted to pH 4.6 with ammonia water (25 weight %). Additionally, 600 g of the cerium oxide slurry (solid matter: 5 weight%) was added thereto, to give a cerium oxide-based CMP polishing slurry(solid matter: 1.0 weight %). The polishing slurry had a pH of 4.8, andthe average particle diameter of the particles in the polishing slurry,as measured by a laser-diffraction particle size distribution analyzerafter dilution to a suitable concentration, was 170 nm.

(Polishing of Insulation Film Layer)

A test wafer for evaluation of shallow-trench-isolation (STI) insulationfilm CMP was polished in the same manner as in Example 1, except thatthe polishing slurry thus prepared was used. The results are summarizedin Table 1.

As described above, when a wafer for evaluation was polished with eachof the CMP polishing slurries prepared in Examples 1 to 4, the convexregion was polished completely and the SiN film was exposed in 200seconds or less, as shown in Table 1. In addition, the difference inthickness between the films remaining in the high-density area (convexregion: 100%) and the low-density area (convex region: 10%) was not morethan 14 nm, suggesting uniform polishing. The level difference afterpolishing was 2 to 10 nm, indicating high smoothness.

Observation of the insulation film surface after polishing under anoptical microscope showed no distinct polishing scratch on the sample inany Example.

Comparative Example Synthesis of Water-Soluble Polymer

480 g of isopropanol and 480 g of deionized water were placed in a3-liter preparative flask and heated to 75° C. while stirred undernitrogen gas atmosphere, and a solution of 560 g of acrylic acid and 40g of 2,2-azobisisobutylonitrile in 500 g of isopropanol was added intothe flask over a period of 2 hours. The mixture was then kept at 75° C.for 3 hours, cooled to give a water-soluble polymer solution. Then onvolatile matter determined was 25weight %. The weight-average molecularweight of the water-soluble polymer obtained, as measured similarly toExample 1, was 25,000 (as polyethylene glycol).

(Preparation of Polishing Slurry)

30 g of the aqueous polyacrylate solution (25 weight %) and 2,370 g ofdeionized water were mixed, and the mixture was adjusted to pH 6.9 withammonia water (25 weight %). Additionally, 600 g of the cerium oxideslurry (solid matter: 5 weight %) was added thereto, to give a ceriumoxide polishing slurry (solid matter: 1.0 weight %). The polishingslurry had a pH of 7.0, and the average particle diameter of theparticles in the polishing slurry, as measured by using alaser-diffraction particle size distribution analyzer after dilution toa suitable concentration, was 170 nm.

(Polishing of Insulation Film Layer)

A test wafer for evaluation of shallow-trench-isolation (STI) insulationfilm CMP was polished in the same manner as in Example 1, except thatthe polishing slurry obtained was used. As a result, a period as long as300 seconds was needed for exposure of the SiN film in the high-densityarea (convex region: 100%), indicating that the polishing speed islower. On the other hand, the SiN film in the low-density area (convexregion: 10%) was also polished completely, indicating the polishingproceeded unevenly according to the pattern density. TABLE 1 ComparativeItem Example 1 Example 2 Example 3 Example 4 Example Cerium oxide (wt.%) 1.0 1.0 1.0 1.0 1.0 Water-soluble Polyacrylic Polyacrylic PolyacrylicPolyacrylic Poly- polymer acid acid acid-methacrylic acid-methacrylicacrylic 0.3% 0.4% acid copolymer acid copolymer acid Mw = 5,000 Mw =3,200 0.3% 0.25% 0.25% Mw = 4,200 Mw = 7,500 Mw = 25,000 Polymerization2,2′-Azobis[2- 2,2′-Azobis[2- 2,2′-Azobis[2- 2,2′-Azobis[2- 2,2′-initiator (2-imidazolin- (2-imidazolin-2- (2-imidazolin-(2-imidazolin-2- Azobis 2-yl)propane] yl)propane]bisul- 2-yl)propane]yl)propane]bisul- isobutylo fate dihydrate fate dihydrate nitrilePolishing slurry 5.0 5.5 5.1 4.8 7.0 pH Polishing period 180 165 180 200300 (second) Residual Convex 148 136 140 150 140 SiN region thickness100% in convex Convex 138 122 128 138 0 region (nm) region 10% ResidualConvex 452 440 430 460 170 SiO₂ region thickness 10% in concave region(nm) Level difference 4 10 7 2 155 (nm)

INDUSTRIAL APPLICABILITY

The present invention provides a polishing slurry and a polishing methodallowing polishing of a silicon oxide film or the like without polishingscratch uniformly at high speed and also allowing easy processmanagement in the CMP technology of smoothening films such as aninterlayer dielectric film, BPSG film, and insulation film for shallowtrench isolation.

1. A CMP polishing slurry comprising cerium oxide particles, adispersant, a water-soluble polymer and water, wherein the water-solublepolymer is a polymer obtained in polymerization of a monomer containingat least one of a carboxylic acid having an unsaturated double bond andthe salt thereof by using at least one of a cationic azo compound andthe salt thereof as a polymerization initiator.
 2. The CMP polishingslurry according to claim 1, wherein the blending amount of thewater-soluble polymer is 0.01 weight part or more and 5 weight parts orless with respect to 100 weight parts of the CMP polishing slurry. 3.The CMP polishing slurry according to claim 1, wherein theweight-average molecular weight of the water-soluble polymer is 200 ormore and 50,000 or less.
 4. The CMP polishing slurry according to claim1, wherein the average particle diameter of the cerium oxide particlesis 1 nm or more and 400 nm or less.
 5. The CMP polishing slurryaccording to claim 1, wherein the blending amount of the cerium oxideparticles is 0.1 weight part or more and 5 weight parts or less withrespect to 100 weight parts of the CMP polishing slurry.
 6. The CMPpolishing slurry according to claim 1, wherein the pH thereof is 4.5 orhigher and 6.0 or lower.
 7. A polishing method of substrate comprising:pressing a substrate having a film to be polished against a polishingcloth of a polishing table; and polishing the film to be polished bymoving the substrate and the polishing table relatively to each otherwhile supplying the CMP polishing slurry according to claim 1 betweenthe film to be polished and the polishing cloth.